1. Field of the Invention
The present invention relates to an image-holding member for holding electrostatic images and/or toner images, and more particularly to an image-holding member having improved surface property, abrasion-resistance and durability, and as well as to an electrophotographic photosensitive member having improved sensitivity, durability, surface property, cleanability, toner-filming resistance and abrasion-resistance. Furthermore, the present invention relates to a display apparatus, for displaying, as observable images, electric image information calculated or read out from electronic computers and image-reading-out apparatuses, and similar other image information stored and memorized in magnetic tapes and microfilms in the form of soft copies. It relates also to a display apparatus attached, as image monitors, to image-forming apparatuses, such as copying apparatuses and office automation apparatuses.
2. Description of the Prior Art
Image-holding layers capable of forming electrostatic images and/or toner images, corresponding to the outputs of various information signals on the surfaces of image-holding members, used for electrophotographic copying apparatuses, laser printers, and image-display apparatuses, are already known. These layers may be formed by various processes. The image-holding members forming electrostatic images and/or toner images include image-holding members with photoconductive layers called electrophotographic photosensitive members and image-holding members without photoconductive layers. The image-holding members are usually composed of supports and image-holding layers thereon.
Electrophotographic photosensitive members may have various structures involved in providing them with predetermined characteristics, or according to the applicable type of the electrophotographic process. These members have a structure which is typified by a photosensitive member having its photoconductive layer on a support, and a photosensitive member having further an insulation layer thereon. Some examples in this regard and described in U.S. Pat. No. 2,860,048, Japanese Patent Publication Nos. 16429/1966, 15446/1963 and 3713/1961, U.S. Pat. No. 3,607,258 and Japanese Patent Publication Nos. 23910/1967, 24748/1968, 19747/1967, and 4121/1961. There are photosensitive members having laminated structures of charge generation layers and charge transport layers. The examples are described in Japanese Patent Laid-Open No. 105537/1964, U.S. Pat. No. 3,837,851, Japanese Patent Laid-Open No. 90827/1976, British Pat. No. 1,453,024, U.S. Pat. No. 3,484,237 and U.S. Pat. No. 3,871,882. Some predetermined electrophotographic processes are applied to electrophotographic photosensitive members, to form electrostatic images which are then developed so as to make them distinctly visible.
There is an image display apparatus with a photoconductive layer, using an electrophotographic process (described in British Patent Publication No. 2114772) in which toner images are formed at the same time of exposure.
Image display apparatuses extensively used hitherto include CRT display apparatuses and liquidcrystal display apparatuses, which are not always satisfactory in respect of resolution, the area of the display image, and observability. Recent progress in office automation apparatuses has required displays with very fine, stationary images for monitors of word processors, microfilm retrieval devices and optical disk memories. In view of this progress, images on the CRT and liquid crystal display apparatuses cannot be regarded as uptodate and adequate because of the screen flicker and dependance on visual angle.
As methods of solving the problems of the CRT and liquid crystal display apparatuses, there may be exemplified a method for forming a toner image at the same time of exposure, using a photoconductive layer as the aforementioned image-holding member (British Patent Publication No. 2114772), a method for giving an electrostatic charge image on the dielectric belt of an image-holding member by means of stylus electrodes to convert the images into a toner image (Japanese Utility Model Laid-Open No. 55061/1982), and a method for forming a latent image on a magnetic recording layer to visualize it on the surface of an image-holding member by use of a toner in the form of magnetic powder or fluid according to the magnetizable signals.
The fact that these display images are superior to those in the conventional electrophotography, electrostatic printing and magnetic printing will be easily understood, since any image transfer process is not involved. The images can be especially excellent for stationary image displays, because the quality of the images is as clear as prints, specially in contrast to the images of the aforementioned universal CRT and liquid crystal display apparatuses.
The problem of a display apparatus exclusively meant for toner images is one of marked contamination of the non-image portions due to qradual adherence of toners and coloring materials for toners on the surfaces of image displays because of the repeated use of the same image-holding member. The displaying process by this method comprises conversion of an information signal into time-series signals, such as light, e.g. laser beams, voltages, and currents in order to form a latent image on the image-holding member, followed by development of the image by means of a toner. Repeated display operations are carried out by erasing the image, which has become unnecessary, and producing another image pattern on the surface of the same image-holding member by the same process once again. Accordingly, contamination on the surface of the image-holding member causes a markedly deterioration in the quality of the image. This problem has presented a serious problem in making this type of display apparatus practical. A method for obtaining an image by a similar process involves the use of an apparatus for giving a print image by transferring on commonly used paper a toner image formed on intermediate masters, as in the aforementioned electrophotographic copying, electrostatic printing, and magnetic printing. The intermediate masters which are repeatedly used in the printing apparatuses, even if contamination on the surfaces of the masters themselves causes no adverse effect on the transferred images, present no problem concerning their practical use. However, on the other hand, if the toner image on the master is used as a display image, the eventuality of contamination will seriously jeopardise the quality of the display.
Image-holding members for the aforementioned image display apparatus require not only suitable physical and electrical characteristics, but also durability and cleanability. Durability is required when the image-holding member is repeatedly used. Cleanability is a requirement for determining the possibility or otherwise of easy removal of a toner adhering to and remaining on the surface of the image-holding member. It greatly affects formation of clear images and prevention of damage to the cleaning mechanism.
Conventional image-holding members have disadvantages, such as unsatisfactory surface smoothness and abrasion resistance, and the presence of background stains due to insufficient cleaning when repeatedly used.
As stated earlier, the electrophotographic photosensitive members have various structures for giving them desired characteristics, or according to the type of the electrophotographic process. The members are exemplified by a photosensitive member having a photoconductive layer formed on a support, and a photosensitive member which has further an insulation layer on the surface thereof. Further, there is another photosensitive member which has a laminated structure in which the photoconductive layer consists of a charge generation layer and a charge transport layer.
Such electrophotographic photosensitive members require not only the electrical characteristics suitable for the electrophotographic process comprising charging, imagewise exposure, development, transfer, cleaning, and removal of charge simultaneous with exposure, but also durability and cleanability. Durability is required when a photosensitive member is repeatedly used. Cleanability is a requirement for determining the easiness of removal of toners adhering to or remaining on the surface on the photosensitive member and greatly affects formation of clear images and prevention of damage to the cleaning mechanism.
In the conventional electrophotographic photosensitive members, the insulating layers for the photoconductive layers are formed from coatings, such as of acrylic or styrene resins. When the photoconductive layer is of laminated structure consisting of a charge generation layer and a charge transport layer, the latter one, beinq the surface layer, uses a styrene resin, or an acrylic resin, or a cellulose resin as the binder for a hydrazone compound or a pyrazoline compound, and these resins constitute the coatings.
Electrophotographic photosensitive members having surface layers using such coatings have unsatisfactory surface hardness and abrasion-resistance, and therefore stains on the background of copy images become increasingly apparent due to insufficient cleaning by any repeated electrophotographic process. Low hardness of the surface layer of the electrophotographic photosensitive member, which comes into contact with the blade of a urethane rubber used in the cleaning process, further decreases the cleanability.
The electrophotographic photosensitive member is basically composed of a substrate and a photosensitive layer. If desired, a subbing layer may be placed between the substrate and the photosensitive layer for the purpose of improving adhesion between the substrate and the photosensitive layer, enhancing the coating property of the photosensitive layer, protecting the substrate, coating the defects on the substrate, protecting the photosensitive layer from any electrical destruction, and improving injection of charges from the substrate to the photosensitive layer.
The subbing layer may be composed of polyvinyl alcohol, polyvinyl methylether, poly-N-vinyl-imidazole, polyethylene oxide, ethylcellulose, methylcellulose, ethyleneacrylic acid copolymer, casein, polyamides, glue and gelatin. The film thickness is in the order of 1-10 .mu. (microns).
Formation of a subbing layer can be an effective means, but it has various disadvantages, such as difficult obtainability of satisfactory raw material, increase in the manufacturing costs because of the many coating processes involved, and the increased items of production control, resulting in the increased costs.
Although the photosensitive layer of the laminated structure generally consists of a charge generation layer and a charge transport layer, both layers are electrically connected to each other, and the charge carrier generated in the charge generation layer, in the presence of an electric field is to be efficiently injected to the charge transport layer.
For this reason, we have conducted various investigations for better charge injection by means of improvement in adhesion or close contact between the charge generation layer and the charge transport layer.